For producing reduced iron, there is conventionally known a method including charging a plurality of reduced iron raw materials, each of which contains carbonaceous reducing agent and iron oxide, into a traveling hearth reduction-melting furnace to treat them. For example, Patent Literature 1 discloses a method including preparing numerous spherical pellets as the plurality of reduced iron raw materials, inserting these pellets successively into the traveling hearth reduction-melting furnace to heat the pellets, and separating the reduced iron (metal iron) produced by the heating from slag to discharge the reduced iron and the slag to outside of the reduction-melting furnace.
The traveling hearth reduction-melting furnace has a hearth movable in a specific direction and a ceiling located over the hearth, each of which is constructed with a refractory such as a brick. On the hearth is provided a hearth covering material for protecting the refractory. In detail, on the hearth, there are continuously performed a series of treatments on the iron oxide, that is, reduction, cementation, melting, aggregation, and slag separation; in order to inhibit the thus treated iron oxide treated from direct contact with the refractory constituting the hearth, the hearth covering material is laid with a suitable layer thickness on the hearth.
As means for charging each of the pellets into the reduction-melting furnace, Patent Literature 1 in FIG. 8 discloses letting each of the pellets fall freely and successively from the ceiling onto the hearth, specifically onto the hearth covering material, through a plurality of supplying units provided in the ceiling.
Patent Literature 2 discloses a charging device provided with a charging inlet that can be tilted so as to descend from a ceiling of the reduction-melting furnace. The charging inlet has an upper inlet, a passageway for letting the pellets descend, and a lower outlet, being capable of being lowered to a position where the lower outlet is close to the hearth, while being inclined.
For producing reduced iron from the plurality of reduced iron raw materials in such a traveling hearth reduction-melting furnace, it is desirable to treat the reduced iron raw materials efficiently in a period of time as short as possible. As effective means therefor, the present inventors have paid attention to promoting good heat input by securing a contact area at which each of the reduced iron raw materials and a high-heat gas in the surroundings thereof make contact with each other and securing a heat-receiving area which is a part of the surface area of the reduced iron raw materials at which area the reduced iron raw materials receive the heat given to the reduced iron raw materials by radiation, and have found out that, from such a viewpoint, the conventional techniques disclosed in Patent Documents 1 and 2 involve important problems.
Specifically, the reduced iron raw materials that are successively charged into the melting furnace by free fall as disclosed in Patent Document 1 include not a few reduced iron raw materials at least a part of which is embedded in the powdery hearth covering material and/or not a few reduced iron raw materials that are stacked onto the preceding reduced iron raw materials. This embedment and/or stacking of the reduced iron raw materials may reduce the contact area at which each of the reduced iron raw materials and a high-heat gas in the surroundings thereof make contact with each other and the heat-receiving area which is a part of the surface area of the reduced iron raw materials at which area the reduced iron raw materials receive the heat given to the reduced iron raw materials by radiation; these may hinder sufficient heat from being input into the reduced iron raw materials.
The technique disclosed in Patent Document 2, though enabling the lower outlet of the pellet charging inlet to come close to the hearth, does not allow powdery hearth covering material for protecting the hearth such as described above to be easily added. If the hearth covering material was spread on the hearth in this technique, the lower outlet of the pellet charging inlet coming close to the hearth covering material would involve considerable turbulence of the gas flow between the lower outlet and the hearth covering material, which could cause considerable scattering of the hearth covering material and embedment of the pellets (reduced iron raw materials) due to the scattering. Furthermore, because of high-temperature gas under the ceiling, large extension of the pellet charging inlet such as described above downward beyond the ceiling has to use a material with a high heat resistance enough to withstand the high temperature, involving considerable increase in the costs. Besides, even with use of such heat-resistant material, the high-temperature environment does not allow the decrease in the reliability of the charging equipment to be avoidable.